1. Field of the Invention
The present invention relates to a radio communication equipment, a transmission power control method therefor, and a program therefor, and more particularly to radio communication equipment for generating transmission power control information corresponding to a comparison result between receiving quality of a signal received from a communication counterpart and target quality, and for transmitting the transmission power control information to the communication counterpart, and to a transmission power control method therefor and a program therefor.
2. Description of the Related Art
In a mobile communication system using a code division multiple access (CDMA) system, plural channels share the same frequency band. Each channel is distinguished by a diffusion code added thereto. Each channel becomes interference noise for other channels, and when a signal transmitted with power more than necessary exists, receiving quality of the other stations is deteriorated. Further, in general, power of a radio wave is attenuated more as a propagated distance thereof gets longer. Still further, a fluctuation of an instantaneous value of received power occurs owing to multipath phasing or the like. Accordingly, it becomes important to control the transmission power of user equipment wirelessly connected to a base station.
In order to follow a change of the number of users and the fluctuation of the instantaneous value of the received power owing to the multipath phasing, which cause the interference as described above, the CDMA system measures a signal-to-interference ratio (SIR) at the receiving side. A measurement-SIR (M-SIR) as a measurement value of the SIR and a target-SIR (T-SIR) as a target value of the SIR are compared with each other, and a transmission power control (TPC) is thus performed by a closed loop to approximate the M-SIR to the T-SIR.
However, the SIR necessary to obtain a block error rate (BLER) representing desired quality changes depending on a change of a moving speed of the user equipment under communication and a change of a propagation environment, which is caused by such a movement. In order to follow the change of the necessary SIR, the CDMA system measures the block error rate BLER, and when the measurement-BLER (M-BLER) as the measurement value of the block error rate BLER is lower than the target-BLER (T-BLER) as the target value of the block error rate BLER, the T-SIR is increased. Meanwhile, when the M-BLER is higher than the T-BLER, the T-SIR is decreased.
The adaptive control on the T-SIR as the target value of the SIR to the block error rate BLER, which is as described above, is referred to as an outer loop power control. A method for the outer loop power control is described, for example, in “W-CDMA Mobile Communication System (original title is in Japanese), Maruzen Co., Ltd., Jun. 25, 2001, pp. 126-128”.
As described above, in the conventional outer loop power control, when the M-BLER is lower than the T-BLER, the T-SIR is increased, and when the M-BLER is higher than the T-BLER, the T-SIR is decreased.
However, there is a channel, in which the block error rate BLER of the control information between the base station and the user equipment cannot be measured, for instance, the channel including a dedicated control channel (DCCH), a stand-alone DCCH, and the like for speech communications. In the channel as described above, the receiving side does not use a transport format combination indicator (TFCI), so the receiving side cannot judge whether or not C-Plane data as the control information is being transmitted from the base station. Here, the C-Plane refers to a call control channel for controlling position registration, transmission, reception, and the like.
For example, it is assumed that a cyclic redundancy check (CRC) for inspecting an error of the C-Plane data is judged to be no good (NG) on the receiving side. In this case, it cannot be judged whether the CRC becomes NG because the C-Plane data is not transmitted or the CRC becomes NG because an electric field is deteriorated though the C-Plane data is transmitted. In the channel as described above, the block error rate BLER calculated based on a CRC judgment result cannot be measured.
Hence, in the case of the channel in which the block error rate BLER cannot be measured, the T-SIR cannot be increased by the conventional outer loop power control even if the quality of the control information between the base station and the user equipment is deteriorated. If it becomes impossible to exchange the control information, the communication is to be disconnected.